The present invention relates to an exfoliated picture projection method, program, and exfoliated picture projection device.
Conventionally, in the course of medical activities such as diagnosis and treatment, medical image information relating to internal organs and created by medical diagnostic imaging apparatuses, such as X-ray diagnostic devices, X-ray CT (computerized tomographic) devices, magnetic resonance imaging devices (MRI) and the like, is subjected to image processing so as to be displayed three-dimensionally, and allow three-dimensional observation for diagnosis or treatment purposes. For example, the following methods are used as three-dimensional display methods for displaying tubular organs, such as the trachea, digestive tract, and even blood vessels within internal organs and the like.
One such method is the parallel projective method in which a tubular organ is externally illuminated by parallel virtual rays, and the tubular organ is projected onto a two-dimensional plane. As shown in FIG. 24, a parallel projective image P1 produced by the parallel projective method is suitable for observing the exterior of a tubular organ, however, the interior of the organ cannot be observed. A perspective projective image P2 is created by the perspective projective method, which sets a point of view in the interior of a tubular organ and illuminates the interior with radial virtual rays from the point of view so as to project an image of the interior of a tubular organ onto a two-dimensional plane. As shown in FIG. 25, the perspective projective image P2 is used as a virtual endoscope since the inside of the tubular organ can be observed as an endoscopic image. Although the inside of the tubular organ can be viewed in the perspective projective image P2, there has been concern that polyps and the like may be overlooked unless the entire interior surface of the tubular organ is closely and minutely examined when making a diagnosis. Furthermore, it has been difficult to observe the backside of folds in the tubular organ walls and the like.
In another method, an exfoliated picture exfoliated on a two-dimensional plane is displayed by projecting a tubular organ to a cylindrical projection surface virtually arranged on the surroundings of the tubular organ, using a cylindrical projection method, or inflected cylindrical projection method. Then, the projection picture is exfoliated by cutting the cylindrical projection surface along its axis (for example, A. Vilanova Bartroli, R. Wegenkittl, A. Konig, E. Groller, “Virtual Colon Unfolding,” IEEE Visualization, USA, 2001, pp. 411-420). As shown in the exfoliated picture P3 of FIG. 26, polyps and the like are readily observable since the inner wall surface of the tubular organ can be seen on a two-dimensional surface.
In the exfoliated picture P3, however, the surface area of a predetermined part on the exfoliated picture is not proportional to the surface area of the actual tubular organ. As shown in FIG. 27, for example, when a tubular organ 50 is inflected, since the inflected part is exfoliated on a two-dimensional plane generated by unrolling the cylindrical projection surface, the inner side of the inflected part is expanded in the exfoliated picture P3 as indicated by the solid arrow, and is displayed larger than the actual tubular organ. In contrast, the outer side of the inflected part is compressed in the exfoliated picture P3 so as to be displayed smaller than the actual tubular organ, as indicated by the dashed arrow. Furthermore, even when the expansion of the inner side and compression of the outer side occurs to the same extent and the surface area in the exfoliated picture and the surface area of the actual tubular organ are equal in total, the exfoliated picture P3 is distortedly displayed since the aspect ratio in the exfoliated picture differs from the actual tubular organ. These distortions have been the cause of misdiagnosis since expanded polyps appear as folds of the interior of the tubular organ, and compressed folds appear as polyps. Although it is now possible to perform medical examinations by visually comparing the exfoliated picture P3 and perspective projective image P2 to confirm polyps in spite of the distortion in the exfoliated picture P3, particular care must be taken when examining conspicuously distorted locations since a polyp may be misidentified as a fold.